Reply #1 Top
from Explorer view, Skin name/Window Borders/Titlebar Buttons - Free form, under section Tab on the right Titlebar Button - Sounds will be currently disabled just enable it from combo box.

Then add your *.wav to Titlebar buttons under Section Tab/Actions Button Sound - Press/Release which ever sounds you have can set them up there.
Reply #2 Top
circling raven
To add to what Voodoo_Freak just wrote, you'll need to add the .wav files to your skins directory before they will be available in Skin studio. Then you can assign the sounds to the buttons.